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The G-TAG software tool was developed under the R&TD on Integrated
Autonomous Guidance, Navigation, and Control for Comet Sample Return, and
represents a novel, multi-body dynamics simulation software tool for studying
TAG sampling.

Comet Spacecraft Concept: Red arrows point to joints, blue arrows to spacecraft body components. The frame used for the simulation and for creating simulation movies is shown in the lower-left corner (x-axis completes coordinate system using the right-hand rule)." class="caption">The G-TAG multi-body simulation tool provides a simulation environment in
which a Touch-and-Go (TAG) sampling event can be extensively tested. TAG sampling requires the spacecraft to descend to the surface, contact the surface with a sampling collection device, and then to ascend to a safe altitude. The TAG event lasts only a few seconds but is mission-critical with potentially high risk. Consequently, there is a need for the TAG event to be well characterized and studied by simulation and analysis in order for the proposal teams to converge on a reliable spacecraft design.

This adaptation of the G-TAG tool was developed to support the Comet Odyssey proposal effort, and is specifically focused to address comet sample return missions. In this application, the spacecraft descends to and samples from the surface of a comet. Performance of the spacecraft during TAG is assessed based
on survivability and sample collection performance.

For the adaptation of the G-TAG simulation tool to comet scenarios, models are developed that accurately describe the properties of the spacecraft, approach trajectories, and descent velocities, as well as the models of the external forces and torques acting on the spacecraft. The adapted models of the spacecraft, descent profiles, and external sampling forces/torques were more sophisticated and customized for comets than those available in the basic G-TAG simulation tool.

Scenarios implemented include the study of variations in requirements,
spacecraft design (size, locations, etc. of the spacecraft components), and the environment (surface properties, slope, disturbances, etc.). The simulations, along with their visual representations using G-View, contributed to the Comet Odyssey New Frontiers proposal effort by indicating problems and/or benefits of different approaches and designs.

This work was done by Milan Mandic, Behcet Acikmese, and Lars Blackmore of
Caltech for NASA’s Jet Propulsion Laboratory.

This software is available for commercial
licensing. Please contact Daniel Broderick of
the California Institute of Technology at
This email address is being protected from spambots. You need JavaScript enabled to view it.. NPO-47199

This Brief includes a Technical Support Package (TSP).

Adaptation of G-TAG Software for Validating Touch-and-Go Comet Surface Sampling Design Methodology (reference NPO-47199) is currently available for download from the TSP library.

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